Thermomechanical Analysis

Thermomechanical analysis (TMA) is a thermal analysis method primarily employed for determining thermal expansion coefficients (CTE) and is closely related to dilatometry.

While dilatometry measures expansion under negligible load, thermomechanical analysis measures expansion under controlled load. It records the displacement of the pushrod that is in contact with the sample as a function of temperature.

Setup of a thermomechanical analyser showing the sample, pushrod and displacement sensor (LVDT)

By applying higher forces and/or using pushrods with a tip (penetration pushrod), TMA can be used to investigate the softening of materials, which is particularly useful for measuring the glass transition temperature (Tg) of polymers.

Compared to the commonly used differential scanning calorimetry (DSC), thermomechanical analysis is considerably more sensitive. Sensitivity can be further enhanced by employing oscillating forces, such as sinusoidal, triangular, or rectangular, resulting in an oscillating response signal.

Detection of the glass transition of an elastomer by TMA with oscillating force; Tg was found at 29°C indicated by a strong increase of the detectors response signal

Additional types of pushrods and measurement setups enable the assessment of parameters like Young’s modulus or the measurement of the coefficient of thermal expansion (CTE) for fibers and thin sheets. In the case of the latter, a specialized sample holder secures the sample, and a minor tension is applied to it.

Different TMA measuring systems

Properties and reactions of Thermomechanical Analysis

Thermomechanical Analysis (TMA) is widely utilized in the field of polymer science to measure the coefficient of thermal expansion (CTE) and examine the stress/strain behavior of fibers and thin sheets. When heating a polymer sample, various phenomena can be observed, including solvent evaporation, curing of uncured portions, rearrangement of polymer chains, and recrystallization, which may result in shrinkage (negative expansion).

The softening behavior and glass transition temperatures (Tg) can also be investigated, primarily by applying an oscillating force.

Standards for Thermomechanical Analysis

1. ISO 11359: Plastics – Thermomechanical analysis (TMA)

  •  Plastics – Thermomechanical analysis (TMA) – Part 1: General principles
  •  Plastics – Thermomechanical analysis (TMA) – Part 2: Determination of coefficient of linear thermal expansion and glass transition temperature

2. ASTM E831 – 19 Standard Test Method for Linear Thermal Expansion of Solid Materials by Thermomechanical Analysis

2. ASTM E2113 – 18 Standard Test Method for Length Change Calibration of Thermomechanical Analyzers

3. ASTM E1363 – 18 Standard Test Method for Temperature Calibration of Thermomechanical Analyzers

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